This invention relates generally to the rotor windings of a dynamoelectric machine, and more particularly, to rotor and rotor end winding cooling in machines with concentric rotor windings.
The rotors in large gas cooled dynamo-electric machines have a rotor body which is typically made from a machined high strength solid iron forging. Axially extending radial slots are machined into the outer periphery of the rotor body at specific circumferential locations to accommodate the rotor winding. The rotor winding in this type of machine typically consists of a number of complete coils, each having many field turns of copper conductors. The coils are seated in the radial slots in a concentric pattern with, for example, two such concentric patterns in a two-pole rotor. The coils are supported in the rotor body slots against centrifugal forces by wedges which bear against machined dovetail surfaces in each slot. The regions of the rotor winding coils which extend beyond the ends of the main rotor body are called xe2x80x9cend windingsxe2x80x9d and are supported against centrifugal forces by high strength steel retaining rings. The section of the rotor shaft forging which is disposed underneath the rotor end windings is referred to as the spindle. For ease of reference and explanation hereinbelow, the rotor winding can be characterized has having a slot end region within the radial slots at the end of the rotor body, and a rotor end winding region that extends beyond the pole face, radially spaced from the rotor spindle. This invention relates primarily to the cooling of the rotor end winding region of the rotor winding.
The rotor coils are disposed in the radial slots of the rotor body for carrying current. At the end winding region, the end turns are suitably connected to form the required current pattern. Because the rotor winding gives rise to resistive heating, certain dynamoelectric machines require additional cooling at the rotor end windings. However, these regions are difficult to cool effectively. In that regard, heat is difficult to remove because the mechanical structure that supports the end winding under high centrifugal loads inhibits the placement of cooling passages, lest the mechanical integrity of the support system be compromised.
Several rotor end winding cooling approaches have been used in the past. One technique for avoiding excessive temperature in the end turns and conductor slot bars includes employing a longitudinal gas groove formed on the surface of the conductor coil to provide a ventilation gas channel. The groove is closed by an adjacent coil and its insulation to retain the gas for flow along the entire length of the channel. Cooling gas enters the field turns from an open cavity via inlet ports at the sides of the turns and then flows longitudinally along the grooves to discharge locations that are typically either radial chimneys in the rotor body or discrete baffled discharge zones under and around the end winding. The gas in these baffled zones is typically discharged either to the air gap (i.e., the gap between the rotor and stator) via machined slots in the pole face, or to the area outside of the centering ring via openings in the centering ring. Some schemes utilize discharges through radial holes in the retaining rings. Some cooling approaches are proposed by Kazmierczak (U.S. Pat. Nos. 6,252,318; 6,204,580; 5,281,877), Kaminski (U.S. Pat. Nos. 6,339,268; 4,709,177), and Staub (U.S. Pat. No. 5,644,179). However, these disclosures ultimately deal with how to effectively design a ventilation circuit for end windings, for instance how to arrange grooves (with different patterns lengths, and the like) to achieve relatively uniform temperature distribution.
As will be understood, the use of ventilation grooves in conductor coils greatly reduces the effective cross-sectional area for current transfer, leading to high current density and accordingly high electrical resistance. Thus, it would be desirable to minimize cooling groove dimensions while satisfying end winding cooling requirements. In an embodiment of the invention, groove dimension is minimized while satisfying end winding cooling requirements by adopting heat transfer enhancement techniques to maximize the heat transfer effect while maximizing the cross-sectional area for a current transfer.
Enhanced heat transfer may be realized by providing a cooling gas passage that has a knurled surface. Such roughness geometries act as vortex generators to increase the rate of heat transfer. Thus, the invention may be embodied in a cooling gas ventilation circuit for an end winding of a rotary machine having a rotor, a plurality of radial slots provided in the rotor, and a plurality of coils respectively seated in the radial slots, the coils each comprising a plurality of radially stacked turns, the coils extending beyond a pole face of the rotor to form an end winding, cavities being defined between adjacent pairs of coils, the ventilation circuit comprising: a cooling gas passage defined in at least one turn of each coil of the end winding, the cooling gas passage extending from an inlet port in communication with the cavity on one longitudinal side of the turn to one of (1) a radial chimney defined through a plurality of the turns of the coil within the respective radial slot and (2) an exit port defined on the other longitudinal side of the turn, the cooling gas passage extending along at least a portion of the longitudinal extent of the turn; and wherein at least a portion of a surface of the cooling gas passage is knurled so as to have a non-planar surface profile for enhanced heat transfer.
In addition or in the alternative, enhanced heat transfer may be realized by providing a cooling gas passage that undulates along its length. With such a passage configuration, the cooling flow changes flow direction periodically along the conductor causing local flow separation and reattachment with the passage side surface. Such disturbances between the flow and walls reduces boundary layer thickness and, as a result, increases surface heat transfer coefficient. Thus, the invention may also be embodied in a cooling gas ventilation circuit for an end winding of a rotary machine having a rotor, a plurality of radial slots provided in the rotor, and a plurality of coils respectively seated in the radial slots, the coils each comprising a plurality of radially stacked turns, the coils extending beyond a pole face of the rotor to form an end winding, cavities being defined between adjacent pairs of coils, the ventilation circuit comprising: a cooling gas passage defined in at least one turn of each coil of the end winding, the cooling gas passage extending from an inlet port in communication with the cavity on one longitudinal side of the turn to one of (1) a radial chimney defined through a plurality of the turns of the coil within the respective radial slot and (2) an exit port defined on the other longitudinal side of the turn, the cooling gas passage extending along at least a portion of the longitudinal extent of the turn; and wherein at least a portion of the cooling gas passage defines a wavy cooling path along a direction of cooling gas flow for enhanced heat transfer.
In order to maximize the heat transfer enhancement effect, it is possible to combine these two techniques, that is provide wavy grooves with knurled surfaces. Thus the invention may further be embodied in a rotary machine comprising a rotor, a plurality of radial slots provided in the rotor, a plurality of coils respectively seated in the radial slots, the coils each comprising a plurality of radially stacked turns, the coils extending beyond a pole face of the rotor to form an end winding, cavities being defined between adjacent pairs of coils, and a cooling gas passage defined in at least one turn of each coil of the end winding, the cooling gas passage extending from an inlet port in communication with the cavity on one longitudinal side of the turn to one of (1) a radial chimney defined through a plurality of the turns of the coil within the respective radial slot and (2) an exit port defined on the other longitudinal side of the turn, the cooling gas passage extending along at least a portion of the longitudinal extent of the turn; wherein at least a portion of a surface of the cooling gas passage is knurled to define at least one of ribs and dimples for enhanced heat transfer, and wherein at least a portion of the cooling gas passage defines an undulating path for enhanced heat transfer.